/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Mutexes: blocking mutual exclusion locks
 *
 * started by Ingo Molnar:
 *
 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 * This file contains the main data structure and API definitions.
 */
#ifndef SEMINIX_MUTEX_H
#define SEMINIX_MUTEX_H

#include <seminix/list.h>
#include <seminix/spinlock.h>
#include <asm/processor.h>
#include <asm/current.h>

struct ww_acquire_ctx;

/*
 * Simple, straightforward mutexes with strict semantics:
 *
 * - only one task can hold the mutex at a time
 * - only the owner can unlock the mutex
 * - multiple unlocks are not permitted
 * - recursive locking is not permitted
 * - a mutex object must be initialized via the API
 * - a mutex object must not be initialized via memset or copying
 * - task may not exit with mutex held
 * - memory areas where held locks reside must not be freed
 * - held mutexes must not be reinitialized
 * - mutexes may not be used in hardware or software interrupt
 *   contexts such as tasklets and timers
 *
 * These semantics are fully enforced when DEBUG_MUTEXES is
 * enabled. Furthermore, besides enforcing the above rules, the mutex
 * debugging code also implements a number of additional features
 * that make lock debugging easier and faster:
 *
 * - uses symbolic names of mutexes, whenever they are printed in debug output
 * - point-of-acquire tracking, symbolic lookup of function names
 * - list of all locks held in the system, printout of them
 * - owner tracking
 * - detects self-recursing locks and prints out all relevant info
 * - detects multi-task circular deadlocks and prints out all affected
 *   locks and tasks (and only those tasks)
 */
struct mutex {
    atomic_long_t		owner;
    spinlock_t		wait_lock;
    struct list_head	wait_list;
};

/*
 * Internal helper function; C doesn't allow us to hide it :/
 *
 * DO NOT USE (outside of mutex code).
 */
static inline struct task_struct *__mutex_owner(struct mutex *lock)
{
    return (struct task_struct *)(atomic_long_read(&lock->owner) & ~0x07);
}

/*
 * This is the control structure for tasks blocked on mutex,
 * which resides on the blocked task's kernel stack:
 */
struct mutex_waiter {
    struct list_head	list;
    struct task_struct	*task;
    struct ww_acquire_ctx	*ww_ctx;
};

/**
 * mutex_init - initialize the mutex
 * @mutex: the mutex to be initialized
 *
 * Initialize the mutex to unlocked state.
 *
 * It is not allowed to initialize an already locked mutex.
 */
#define mutex_init(mutex)						\
do {									\
    __mutex_init(mutex);				\
} while (0)

#define __MUTEX_INITIALIZER(lockname) \
        { .owner = ATOMIC_LONG_INIT(0) \
        , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
        , .wait_list = LIST_HEAD_INIT(lockname.wait_list) }

#define DEFINE_MUTEX(mutexname) \
    struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)

extern void __mutex_init(struct mutex *lock);

/**
 * mutex_is_locked - is the mutex locked
 * @lock: the mutex to be queried
 *
 * Returns true if the mutex is locked, false if unlocked.
 */
static inline bool mutex_is_locked(struct mutex *lock)
{
    return __mutex_owner(lock) != NULL;
}

/*
 * See kernel/locking/mutex.c for detailed documentation of these APIs.
 * Also see Documentation/locking/mutex-design.txt.
 */
extern void mutex_lock(struct mutex *lock);
extern int mutex_lock_interruptible(struct mutex *lock);
extern int mutex_lock_killable(struct mutex *lock);
extern void mutex_lock_io(struct mutex *lock);

#define mutex_lock_nested(lock) mutex_lock(lock)
#define mutex_lock_interruptible_nested(lock) mutex_lock_interruptible(lock)
#define mutex_lock_killable_nested(lock) mutex_lock_killable(lock)
#define mutex_lock_nest_lock(lock) mutex_lock(lock)
#define mutex_lock_io_nested(lock) mutex_lock(lock)

/*
 * NOTE: mutex_trylock() follows the spin_trylock() convention,
 *       not the down_trylock() convention!
 *
 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
 */
extern int mutex_trylock(struct mutex *lock);
extern void mutex_unlock(struct mutex *lock);

extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock);

/*
 * These values are chosen such that FAIL and SUCCESS match the
 * values of the regular mutex_trylock().
 */
enum mutex_trylock_recursive_enum {
    MUTEX_TRYLOCK_FAILED    = 0,
    MUTEX_TRYLOCK_SUCCESS   = 1,
    MUTEX_TRYLOCK_RECURSIVE,
};

/**
 * mutex_trylock_recursive - trylock variant that allows recursive locking
 * @lock: mutex to be locked
 *
 * This function should not be used, _ever_. It is purely for hysterical GEM
 * raisins, and once those are gone this will be removed.
 *
 * Returns:
 *  - MUTEX_TRYLOCK_FAILED    - trylock failed,
 *  - MUTEX_TRYLOCK_SUCCESS   - lock acquired,
 *  - MUTEX_TRYLOCK_RECURSIVE - we already owned the lock.
 */
static inline /* __deprecated */ enum mutex_trylock_recursive_enum
mutex_trylock_recursive(struct mutex *lock)
{
    if (unlikely(__mutex_owner(lock) == current))
        return MUTEX_TRYLOCK_RECURSIVE;

    return mutex_trylock(lock);
}

#endif /* SEMINIX_MUTEX_H */
